Abstract
The molecular dynamics of discotic liquid crystalline hexa-peri-hexabenzocoronenes (HBC-C-10,C-6 and HBC-C-14,C-10) with long alkyl side chains branched in close vicinity to the HBC aromatic core were studied by dielectric spectroscopy. The two compounds display a weak dipolar relaxation (a-process) manifested by a Vogel-Fulcher-Tammann (VFT) dependence and have almost the same glass temperature (similar to 215 K) in excellent agreement with the value from differential scanning calorimetry. The origin of this process is the freezing of the in-plane disc rotation. Controlled experiments revealed that the weak dipole moment associated with the a-process is due to oxidation.